Erodium sp

Doesn't seem to match.

My guess would be something in the mustard family. Looks like it might not be long before it starts flowering. Should be easier to ID then.

Yup. I always get excited and try to ID early, because I like to go back later if it's something good. But those early rascals can be difficult :). Thanks lycopus.

The shape and texture are reminiscent to me of a Senecio jacobaea which has had a dose of weedkiller. Is this a ridiculous notion?

Bottom right are some dead flower heads which look like Asteraceae. Are they associated with this plant or the one next to it?